A wrapper around sed for safe automated find&sed-ing

fsed returns with exit code 42, if PATTERN wasn't matched and thus ACTION didn't happen. Also supports a mode where exit code is 42 unless PATTERN was matched exactly N times.

Example usage: fsed '/foo/' 's//bar/' baz.txt

Detailed explanation of the mechanism: https://stackoverflow.com/a/15966279

Script based on stripped down template: https://gist.github.com/Ithanil/b72d61091b73cd8cb0c33de3de593834

1. Substitute pattern and verify:

fsed '/foo/' 's//bar' baz.txt && echo "Found" || "Not found"

2. Delete pattern and verify number of matches

fsed -c 1 '/foo/' 'd' baz.txt && echo "Exactly 1 match" || echo "Not exactly 1 match"

3. Substitution with different pattern / action delimiters:

fsed '\|foo|' 's!!bar!' baz.txt

4. (Caveat!) Append a line (requiring explicit line breaks):

fsed '/foo/' 'a\
appended bar line
' baz.txt

5. In-place edit without following symlinks (i.e. default sed behavior):

fsed -i --no-follow-symlinks '/foo/' 's//bar' baz.link